This project is supplemental to a three year project of the same title. Major goals of the original project were to determine conditions under which simple lipid bilayer vesicles (l) undergo fusion with themselves, and (2) mimic the membrane-associated activities of some enveloped viruses, namely, cell agglutination, fusion with the cell membrane, lysis of erythrocytes, and induction of fusion of cultured cells. By kinetic tests evidence was found for fusion of some vesicles with themselves but others were found to exchange lipid molecules without fusing. The discovery of the latter process, which had not previously been recognized, added a new dimension of complexity to the study of membrane interactions. Lipid vesicles were found to mimic the membrane-associated activities of paramyxoviruses. Electron microscopy revealed that at least some vesicles fused with cell membranes, but it could not be proven that exchange or transfer of lipids from vesicles to cell membranes did not account for some of the effects observed. New methods are proposed in this application which will provide critical tests of the mode of interaction of membranes with other. A sensitive assay for fusion will depend upon the production of a fluorescent compound upon mixing of the internal compartments of the production of a fluorescent compound upon mixing of the internal compartments of the entities (cell or vesicle) involved. Assays for transfer of lipid from vesicle membranes to cell membranes will be based upon detection of an antigenic lipid (originally in the vesicle) in the cell membrane using a fluorescent antibody. The possibility of engulfment of vesicles by erythrocytes will also be tested. Each of these new methods will be applied to vesicles having a variety of lipid compositions in order to first, determine how much the various modes of membrane interaction (fusion, monomolecular transfer, engulfment) contribute in a given situation, and second, to develop an effective new set of "reagents" that can be used to deliver foreign materials to, at will, the membrane, cell sap, or lysosomes of cells.